Among conventional technologies is a printing apparatus capable of reliable, high-speed printing while enabling a reduction in planar installation space for the apparatus (see, e.g., Patent Document 1). According to Patent Document 1, as depicted in FIG. 1, engine units respectively making up each printer can be stacked vertically.
Another conventional technology is a multiprint system having multiple printer units carrying out photograph printing (see, e.g., Patent Document 2). The multiprint system of Patent Document 2 includes multiple supplementary-information recording apparatuses capable of printing an image and recording supplementary-information.
Yet another conventional technology is an image recording apparatus having multiple tiers of image recording units to improve processing efficiency (see, e.g., Patent Document 3). The image recording apparatus of Patent Document 3 includes multiple ink jet recording units and a back printing unit.    Patent Document 1: Japanese Patent Application Laid-Open Publication No. H08-211673    Patent Document 2: Japanese Patent Application Laid-Open Publication No. 2004-42311    Patent Document 3: Japanese Patent Application Laid-Open Publication No. 2003-94748